In U.S. Pat. No. 4,312,278 referenced above, the furnace system is provided with a substitute for the oil burner gun or other conventional firing means, in the form of a wood-type fuel "gun" or burner for retrofitting and firing conventional furnaces or for use in a new independent furnace. For use in retrofitting, the conventional oil burner gun or other firing means is removed one stage from the furnace and may be fitted to the wood-type fuel burner "gun" for initiating combustion of wood-type fuel fragments such as wood chips, continuously fed into the wood fuel "gun". The wood-type fuel fragments or wood chips are "trickle" fed for combustion of the solid fuel at a rate to produce substantially the heat equivalent of the oil burner gun or other firing mechanism associated with the conventional furnace.
The foregoing patent application also described control circuitry for automatic control over the feeding and firing process and safety features which address the problems of continuous feeding and combustion of wood fuel fragments. By these expedients the disclosed invention permits combustion of wood in central heating furnaces with all the incidents and advantages of oil fired systems. A variety of automatic arrangements for safely feeding the fragments of wood-type fuel into the wood fuel "gun" and for safely burning the fuel in the combustion chamber are disclosed and the disclosure of this patent application is incorporated herein by reference.
Ignition of the wood fuel and solid fuel fragments in the furnace system of U.S. Pat. No. 4,312,278 is accomplished by means of an oil burner gun, motor and firing means received at the side of the wood fuel combustion chamber, generally positioned under a wood fuel supporting grate, and automatically controlled and operated to initiate wood fuel combustion. Once firing of the wood is established the oil burner gun is cut off and the furnace output is achieved solely by wood-type fuel combustion.